The invention relates to a constant velocity fixed joint which comprises an outer part, an inner part, a cage, balls and a control element. The outer part comprises a first longitudinal axis and a cavity centered on the axis. The inner face of the outer part is provided with outer running grooves which are circumferentially distributed around the first longitudinal axis. The inner part comprises a second longitudinal axis and, in its outer face, is provided with inner running grooves which are distributed around said second longitudinal axis. The number of inner running grooves corresponds to the number of outer running grooves, with the inner running grooves being arranged opposite the outer running grooves. Furthermore, the inner part is provided with an outer spherical face. The outer running grooves and inner running grooves are positioned opposite one another in pairs, and arranged in meridian planes relative to the associated longitudinal axis and extend in an undercut-free way from a first joint end.
The cage is provided with a hollow spherical partial face by means of which it is guided on the outer spherical face of the inner part. The cage is provided with windows which are circumferentially distributed in accordance with the outer running grooves and inner running grooves. The windows accommodate balls which engage the opposed running grooves for the purpose of transmitting torque. For this purpose they project radially outwardly and inwardly from the cage. The control element is supported on the inner part on the one hand and on a supporting element on the other hand.
U.S. Pat No. 5,376,052 describes such a constant velocity fixed joint wherein the control element comprises a spherical control face which engages a cavity of the inner part, which cavity is centered on the second longitudinal axis. The cavity forms a hollow spherical contact face, with the spherical control face resting thereagainst. Furthermore, the control element comprises a face which extends at a right angle relative to the first longitudinal axis and which supports the control element against a correspondingly extending face of the outer part in a way so as to be radially adjustable relative to the first longitudinal axis. Between the outer face of the cage and the inner face of the cavity of the outer part there is no area contact. In this way, any heat introduced into the inner part while the balls are transmitting torque only has to travel a short distance to reach the sliding region between the control element and the inner part.
U.S. Pat No. 5,453,052 describes a constant velocity fixed joint wherein the outer part and the inner part are provided with running grooves for receiving torque transmitting balls, which running grooves extend in an undercut-free way from one opening end. By means of its spherical outer face, the cage is supported in one direction against supporting elements fixed to the outer part in the region of the opening end. The supporting element is arranged in the region between two circumferentially adjoining outer running grooves. They extend wedge-like into the gap between the cylindrical part of the inner face of the cavity of the outer part and the spherical outer face of the cage. The inner part is supported in the direction opposed to the above-mentioned direction against a spherical dish-like holding element which rests against a spherical outer face of a ball cup in the cavity of the outer part. Otherwise, there is no contact between the outer face of the cage and the outer part. Contact is limited to the supporting elements secured to the outer part. There is no contact between the cage and the outer face of the inner part. Therefore, under torque, the cage is not supported on the inner part in the direction of the longitudinal axis of the outer part, but only on the small supporting elements and, via the holding element, on the outer part, because the outer part and inner part are loaded in opposite directions in the sense of being moved apart. This design leads to high loads andxe2x80x94because of the design of the supporting elementsxe2x80x94to considerable friction.
It is the object of the invention to provide a low-friction constant velocity fixed joint wherein the losses during operation are correspondingly low.
In accordance with the invention, the objective is achieved by providing a constant velocity fixed joint wherein the outer tracks and inner tracks extend from a common first joint end in meridian planes in an undercut-free way and wherein the balls are supported on the window faces of the windows which are arranged near the first joint end. The outer face of the cage is arranged relative to the inner face of the cavity of the outer part in such a way that there exists a distance therebetween over the entire articulation range. Furthermore, the control element is provided with a spherical control face and with a guiding face. The proposed supporting element comprises a hollow spherical contact face against which the control element is supported by means of its control face. Furthermore, the control element is supported by means of its guiding face on a supporting face of the inner part, which supporting face is arranged in such a way that the second longitudinal axis of the inner part is positioned perpendicularly thereon. The supporting element is secured to the outer part or to a component connected to the outer part. The control element and the supporting element are arranged towards the first joint end from which the outer running grooves and inner running grooves extend in an undercut-free way.
The advantage of such a design is that the forces resulting from the transmission of torque at all angles of articulation are advantageously supported via the control element and the supporting element. There exists a further advantage in that, as compared to an assembly wherein the control element is supported against a hollow spherical face of the inner part, it is possible to reduce the number of faces which have to be produced accurately on the inner part. Furthermore, as compared to such a low-friction joint, the amount of friction is reduced even further.
Clear guidance is obtained because support is provided in one direction only and there is no expansion effect, so that there is no risk of jamming. In consequence, the components can be set advantageously relative to one another in the radial direction, taking into account the construction tolerances occurring. The shape of the outer ruing grooves and inner running grooves, and in particular, the way in which they extend from the first joint end towards the second joint end, is selected in such a way that, in all joint angle situations, the balls, when under torque, apply a force to the cage in the sense of applying a load to the window faces close to the first joint end, on which window faces the balls are supported. In this way it is ensured that the cage, by means of its hollow spherical face, is always held in contact with the outer spherical face of the inner part. Centering relative to the outer part in the radial direction is effected entirely by the balls, and in the axial direction, the unit of inner cage part and control element relative to the outer part is achieved by supporting same on the supporting element secured to the outer part. By classifying and dimensioning the components relative to the theoretical articulation center it is thus possible to ensure that all components match one another in such a way that they come as close as possible to the optimum alignment of their operating faces relative to the theoretical joint articulation center.
According to a further embodiment of the invention it is proposed that the control element is dish-shaped. In this way it is possible to achieve a component which can be produced cost-effectively by a non-chip-forming method with a high degree of repeat accuracy.
The supporting element, too, can be provided as a part formed from sheet metal. It is preferably firmly connected to the outer part, so that a pre-assembled unit is achieved.
In addition to the advantageous supporting conditions achievable, it is also possible to provide friction-reducing means between the control face and the contact face.
For a first embodiment it is proposed that the friction-reducing means comprise lubricating grooves which are annular in shape and are connected to a lubricant reservoir by means of lubricating bores. The dish-shaped chamber of the control element can be used as the lubricant reservoir.
The advantage of this embodiment is that it is possible to achieve high sliding speeds between the control face and the contact face when the joint rotates in an articulated condition. By selecting a suitable surface ratio between the lubricating grooves and the area of surface contact which occurs between the control face and the contact face when the outer part and inner part are in an aligned condition relative to one another, the high sliding speeds lead to a hydrodynamic condition of lubrication. The amount of friction thus becomes negligibly small, which means that overall, it is possible to achieve a long service life and reduce any transmission losses to a minimum. This also ensures a high degree of efficiency which, in turn, means that less heat is generated, so that it is possible to lubricate the constant velocity fixed joint with cheaper greases such as used for rolling contact bearings, for example.
Alternatively, the friction reducing means can be provided in the form of a rolling contact bearing which comprises a bearing cage for guiding bearing balls which, by the bearing cage, are rollingly held between the control face and the contact face. In this way it is possible to achieve supporting conditions and friction conditions which are similar to those of rolling contact bearings.
Particularly advantageous conditions can be achieved if the bearing cage is connected to the cage, so that the bearing cage controlled by the cage necessarily follows the movement of the latter. Two preferred embodiments of the invention are diagrammatically illustrated in the drawing wherein.